Hot gas generating installation



y 13, 1965 R. H. F. MARCHAL ETAL 3,194,295

HOT GAS GENERATING INSTALLATION Filed June '7, 1963 m m M BY cm, W um ATTORNEYS United States Patent 3,194,295 HOT GAS GENERATING INSTALLATIGN Raymond Hippolyte Firmin Marchal, Paris, and Pierre Servanty, Aulnay-sous-Bois, France, assignors to secrete Nationale dEtude et de Construction dc Moteurs dAviation, Paris, France, a company of France Filed June 7, 1963, Ser. No. 286,375 Claims priority, application France, June 9, 1962,

2 Claims. Cl. 158-4) This invention relates to installations for generating streams of hot gas.

It is an object of the invention to provide a hot-gas generating installation which will supply a flow of hot gas at a relatively high rate, with the temperature thereof undergoing considerable periodic variations. It is a further object of the invention to provide such an installation with which the flow of gas supplied will be subject also ,to periodic variations in pressure and specific mass.

It is a further object of the invention to provide an installation which will supply a substantially continuous flow of gas comprising alternating sections or bursts of different temperatures.

According to the invention there is provided a hot gas generating installation comprising at least two (and preferably three or more) tubular burners arranged in succession, a first of said burners being of the acoustic resonance type, adapted to effect periodic combustion of fuel and combustion-supporting medium supplied thereto under pressure, so as to produce a stream of hot gas varying periodically at a frequency determined by the dimensions of said first burner and the pressures at which fuel and combustion-supporting medium are supplied, and a second of said burners being adapted to receive exhaust gas supplied thereto by said first burner, to effect combustion in said second burner.

Advantageously the following burner or burners is or are designed and shaped so as not to disturb, by their own operation, the frequency set up by the first burner.

The relative disposition and the arrangement of the successive burners are advantageously such that the hot gases discharged by one burner in the direction of the following burner effect at least the partial supply of the latter with combustion-supporting medium by an induction or pump effect, and the ignition of the following burner by pilot flame effect, that is to say, the exhaust gases supplied to the said following burner by the said one burner are at such a temperature that fuel is spontaneously ignited in the said following burner.

In a preferred embodiment of the invention, the burners extend, over a considerable part of their length, inside gas-tight chambers filled with compressed air or other supporter of combustion under pressure, serving to feed the burners.

The description which follows with reference to the accompanying drawing is given by way of non-limitative example only but will make clearly understood how the invention may be carried into effect, the details appearing both from the text and from the drawing forming part of the said invention.

The single figure of the drawing is a diagrammatic view in longitudinal section of one form of installation constructed in accordance with the invention.

Referring to the drawing, the installation comprises a series of three tubular burners 1, 2 and 3 arranged one after the other on the same axis XY and extending, over the major parts of their lengths, in gas-tight chambers 4 and 5 supplied with compressed air or other supporter of combustion under pressure, by way of conduits 6 and 7.

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The leading burner 1, which includes a combustion chamber 8, is closed at its forward or upstream end and is connected in the downstream direction by a short convergent portion 9 to a tuyere it) which opens into the chamber 4. The combustion chamber 8 is provided with injectors 11 which are located close to its forward end, adjacent a sparking plug 12, and are supplied with fuel through a pipe 13. Pipe lines 14 deliver compressed air into the combustion chamber 8 through one or more peripheral jets. Advantageously there are four jets arranged in opposite pairs, so as to produce good distribution of the supporter of combustion and strong turbulence in the region of the injectors 11.

This leading burner 1 is of the so-called acoustic resonance type, that is to say, combustion of fuel takes place therein in a spontaneously periodic manner, the frequency being a function of the geometrical dimensions of the burner and, in particular, a function of the total length of the burner and of the ratio of the volumes of the combustion chamber 8 and the ejection tuyere 10, and also a function of the pressures at which the fuel and the supporter of combustion are supplied. In fact:

For a given ratio of the volume of the combustion chamber to the volume of the tuyere, the shorter the burner the higher the frequency;

For a given total length, the frequency is reduced as the volume of the chamber is increased in relation to that of the tuyere;

Finally, for any given set of geometrical dimensions, the frequency increases when the pressures at which the supporter of combustion and the fuel are supplied are raised.

Of course, there are limits to the possible frequency variations, these limits being imposed by the stability of the self-igniting combustion and being a function of the nature of the fuel employed and of its ignition or firing time. Beyond these limits, resonant operation is unstable, or even impossible, in which case continuous combustion of low thermal efficiency takes place in the burner.

In practice, depending on the value of the geometrical parameters and of the supply pressures, the frequency of combustion of such a burner may vary from a few cycles per second to 600 cycles per second and even more where a fuel having a small ignition time is used. Thus the frequency of combustion can be adjusted within very wide limits, according to requirements.

The intermediate burner 2, located downstream of the previously mentioned burner 1, comprises basically a convergent portion 15 of evolute form leading into a divergent conical portion 16 terminating in an evolute widened portion 17 which connects the divergent conical portion 16 with a combustion chamber 18, the chamber 18 being generally cylindrical and extended by a short tuyere 19. Advantageously the latter is terminated by a short convergent portion 20. In the zone where the divergent portion 17 opens into the combustion chamber there is located .a fuel feeding system consisting of one or more injectors 21.

The dimension of the intermediate burner 2 will be chosen in dependence upon those of the leading burner 1 and also upon the flow characteristics desired for the nominal supply pressure of the supporter of combustion (that is to say, the pressure prevailing in the chamber 4). However, in designing the burner 2, it is of advantage to bear in mind the following considerations so that a departure may be made, as far as is possible, from the normal dimensional characteristics of pulsatory combus tion chambers, in order that the working rhythm imposed by the leading burner 1 shall not be disturbed:

The total length of the burner 2 will generally be less da than five times the diameter of its. combustion chamber The length of the divergent feed portion -16-17 will be ofthe same order of magnitude as the sum of the lengthstof the combustion chamber 18, the ejection tuye re 19 and theconvergent portion 20;

The length of the combustion chamber 18. will be of the same. order of magnitude as thelength of'the tuyere 19; while the diameter of the latte-r'will be more than 70% ofthe diameter of the combustion chamber;

The angle of the conical .part of thedivergent portion 16, relatively to the central axis, will be of the order of 8. and its smallest cross-section will have an area greater than that of the cross-section of the tuyere 10 of theleadin'g burner 1.

The final or tail burner 3 .is of similar form to the burner 2. Inthis case we again find an evolute convergent portion 22, a conical divergentv portion 23, 'a'connecting diver-gent portion 24. and a cylindrical combustion. chamber connected by a convergent portion. 26

. gen feed nozzles 29 are advantageously I provided upstream of the fuel injectorsZSin theconical divergent portion 23. a

For determining the dimensions of considerations:

The sum of the lengths of the divergent portions 22,. 23 and 24, the combustion chamber 25 and the-connect ing convergent portion 'Zdshould besrnallerbt'han the ength of tuyere 27; v j

The length of the combustion chamber 25, should be less than twice its diameter; a

The conical. divergent portion 23 hasan angle of the orderof 8; relatively to the central axis andit'ssmaIlest cross-section has an area larger than the area" of the cross-section of the ejection'tuyere 19 .of the intermediate burner 2; i i 7 Each chamber 4 or 5 may be formed by a cylindrical element terminating at its ends in two hemispherical por tion-s having orifices. limited by flanges. To the latter the tail burner 5,- it 'is'of advantage to take into account the following there are fixed matingtlanges carried by the burners and forming the fixing means :for the latter.

The arrangementwhich has just been described operates in the following manner: 7

As has already been mentioned, the leading burner 1 V (hereinafter called the acoustic burner) operates ata given frequency which can be regulated.

Y The kinetic energy of thegas periodically ejected by the tuyere 10 of the burner 1 ensures that the intermediate burner2 (hereinafter called the non-resonant burner) periodically receives supporter of combustion from the chamber 4, by a pump action in accordance with the' well-known phenomenonwof pulsed dilution. When sup.- port-er of combustion fed into the burner 2 in this way wayycombustion takes place in the non-resonant burner 2 at the frequency determined by the periodic combustion in the acoustic burner 1. 7

'The' advantage of arranging the two types of burners The orifices are designed so as to permit easy mounting and removal ,of' the burners.

in .succession arises from the nance burner 1 is necessarily of small'dimensions in or-f der that the 'frequency of combustion should, as is-desirable; exceed some hundred cyclesipeii,secondr The small volume, imposed onthis acoustic. burner 1 hasthe result of limiting. rather closely thef'mass and rate of floyv of gas which it is capable of-producing. On the 'other.;

hand, since the performance of'thegnonresonant burner 2 is notlimitedby the requirements of self-feedingand self-ignition, it can-considerablyincreasethe mass and rate of fiow of the gases subjected toithetherm odynamic process. In brief, it can be said that the acoustic burner 1 determines the frequency of the periodic combustion while; the. nonresonant: burner 2 determines; the rate "of flow or delivery. Thus itis possible for an? installation only'two burnersifdesiredc k V a I a a As regards the installation's'hown in the -drawings, the

constructed inaccordance with the; invention to include energy of the gases which issueperiodically from :the burner 2fand exert an induction eifect. This supporter,

ofcombustion is enriched with oxygen at 129,,as it passes through the int'aikenozzle '23 er the post-combustion burner; I i

The periodic combustion OfthefueLimthe presenceof 7 air. enriched with oxygen andheated by'admixture with. Y the. hot gases ejected by the non-r'esonant burner 2, as well as by heat transmitted'by the walls of the vbnrners 2 and 3 by convection and radiation, makes it possible to obtain, at 11-116 frequency determined by the acoustic;

burner -1, the periodic vproductionof masses area at high temperature which-are supplied in the form of. hot" bursts in the how emerging from the. ejection tuyere'z'l."

The function of the tgas-tight chambers 4 and S is to permitthe hon-resonant burner 2 and the post-combustion burner 3 Lto'be suppliedwith supporter of combustion at elevated pressure} In the caseof either chamber, thetsupporterof combustion may be ordinary compressed" air orjcompressed air enri'ch'ed with oxygen, r

Moreover; these chambers considerably reduce the; ther mal lossesof the installation, particularly when they are provided. with :thermal. insulation sinceptheacalories of heat transmitted by'thewallsofione burner are almost wholly recovered by. the supporter of combustionwhich is usedat the followingcombustion stage. 1. a

Finally, these chamber-shave a silencing function, which is particularly important sincethe noise leivelfof periodic burners is 'always high by. reason of the strong pressure V vibrations which they set. up; 7 a

' It is to be observed that with such aninStallatioha large number tofadjustable parameters isavailable. In 7 addition to the geometricaldimensions cnwhich'the; frequency depends, it'is. possible-to regulaterthe pressure'.- andconsequently the rate of flow-of the fuel feeding the;

three burners. Likewise the threeisystems for supplying supporter fcombnstion-to the respective burners arcindividually adjustable in pressure. 'In this respect, it isv desirable thatthe pressure at whichthe leading burner 1 is supplied withfsupporter of combustion, should fbe lhigher thanthe pressure of the supporter 'of combustion contained in the chamber .4 and supplying the intermedi' ate burner 2, Ithislatter pressure in turn being higher than the pressure ofthe supporter of combustion contained in,

the chamber 5 andlintended for the tail burner: 3.?1 a

' It is. also possiblegto effectregulationlby varying the operatingztemperatures. 'Thus,-the supporter of combustion can be pre-heated before admission into the chambers 4 and .5 .tofselected temperatures which,'however, must of course be vcompatiblewith the behaviour of the. materials used in the' construction-of the installation.-

Finally, .the 'rate of enrichment of the supporter; of V combustion with oxygen for the purposes of, post-combustion in the chamber: 3 can be gegula'ted'by modifying its tact thatQthe acoustic resoy' supply pressure, this having a direct influence on the temperature reached by the hot sections or bursts of the flow.

In short, it will be seen that it is easily possible in this way to fix the duration of the alternately very hot and less hot. flow bursts which the generator will deliver through its outlet tuyere 27.

The gas generator of the present invention is susceptible of many applications, the most interesting of which will, it appears, he in the fields of testing refractory materials, of experimental studies of non-uniform flow and of the direct conversion of heat energy into electrical energy by so-called magneto-gas-dynamics.

For this last application, one of the burners will generally be equipped with a complementary feed device by means of which a solution of a readily ionisable substance, such as potassium, is introduced into the flow.

It is obvious that modifications may be made in the form of installation which has just been described, in particular by substituting equivalent technical means, without thereby departing from the scope of the present invention as defined by the appended claims.

What we claim is:

1. A hot gas generating installation comprising a first, a second and a third intermittent-combustion duct means axially arranged in series, fuel injector means in each of said duct means, each of said duct means having a discharge nozzle, inlet passage means in said second duct means positioned adjacent the discharge nozzle of said first duct means, inlet passage means in said third duct means positioned adjacent the discharge nozzle of said second duct means, said inlet passage means of said second and third duct mean arranged to collect the gases discharged from the discharge nozzles of said first duct means and said second duct means respectively and cooperating therewith to produce an injector effect inducing ambient fluid into said second and third duct means, a gas-tight casing surrounding and enclosing a substantial part of said second and third duct means including the discharge nozzle of said second duct and the inlet passage means of said third duct means, oxygen supply means in said third duct means, and means for supplying combustion-supporting gas under pressure into said gas-tight casmg.

2. Installation as claimed in claim 1, comprising further a gas-tight casing surrounding and enclosing a substantial part of the first and second duct means including the discharge nozzle of said first duct means and the inlet passage means of said second duct means, and means for supplying combustion-supporting gas under pressure into said last mentioned gas-tight casing.

References Cited by the Examiner UNITED STATES PATENTS 2,635,421 4/53 Blum 158-4 X 2,923,348 2/60 Fraser 158--4 FOREIGN PATENTS 801,812 9/58 Great Britain.

OTHER REFERENCES German printed application No. 1,071,878, printed December 1959.

JAMES W. WESTHAVER, Primary Examiner.

MEYER PERLIN, Examiner. 

1. A HOT GAS GENERATING INSTALLATION COMPRISING A FIRST, A SECOND AND A THIRD INTERMITTENT-COMBUSTION DUCT MEANS AXIALLY ARRANGED IN SERIES, FUEL INJECTOR MEANS IN EACH OF SAID DUCT MEANS, EACH OF SAID DUCT MEANS HAVING A DISCHARGE NOZZLE, INLET PASSAGE MEANS IN SAID SECOND DUCT MEANS POSITIONED ADJACENT THE DISCHARGE NOZZLE OF SAID FIRST DUCT MEANS, INLET PASSAGE MEANS IN SAID THIRD DUCT MEANS POSITIONED ADJACENT THE DISCHARGE NOZZLE OF SAID SECOND DUCT MEANS, SAID INLET MEANS OF SAID SECOND AND THIRD DUCT MEAN ARRANGD TO COLLECT THE GASES DISCHARGED FROM THE DISCHARGE NOZZLES OF SAID FIRST DUCT MEANS AND SAID SECOND DUCT MEANS RESPECTIVELY AND COOPERATING THEREWITH TO PRODUCE AN INJECTOR EFFECT INDUCING AMBIENT FLUID INTO SAID SECOND AND THIRD DUCT MEANS, A 